The 3rd generation partnership project (“3GPP”) is currently studying a next-generation 3GPP system to be connected to existing 3GPP systems, the Internet, wireless local area networks (“WLANs”) and so on. FIG. 1 shows a network architecture of a next-generation 3GPP system (i.e. evolved 3GPP system) (Non-Patent Document 1).
Next-generation 3GPP system 10 shown in FIG. 1 is comprised of other 3GPP systems (including existing 3GPP systems), non-3GPP systems (including WLAN systems) and a plurality of access gateways (hereinafter “ACGWs”) 20-1 to 20-n connected to the Internet and a plurality of enhanced Node Bs (hereinafter “eNode Bs”) 30-1 to 30-n accommodated in these access gateways.
Although it is currently under study by the 3GPP, basically, eNode B 30 directly accommodates radio terminal apparatuses (i.e. user equipment, or hereinafter “UEs”) and provides radio access functions between eNode B 30 and UEs. ACGW 20 accommodates a plurality of eNode Bs 30-1 to 30-n and transmits/receives packets between eNode Bs 30-1 to 30-n and other ACGWs. Furthermore, ACGW 20 provides mobility functions and so on for when UEs move between the eNode Bs accommodated in ACGW 20. For example, when a UE moves from eNode B 30-1 to eNode B 30-2 accommodated in ACGW 20, ACGW 20 switches the path from source eNode B 30-1 of the UE to destination eNode B 30-2. ACGW 20 then transmits a data packet received from another ACGW to eNode B 30-2 to which the path is set, and transmits a data packet transmitted from this eNode B 30-2 to another ACGW connected to the eNode B that accommodates the UE of the destination of the data packet. Although there are cases where a path is tentatively set directly from eNode B 30-1 to eNode B 30-2 and data directed to a UE is directly transferred from eNode B 30-1 to eNode B 30-2, eventually, ACGW 20 switches the path.
Next, the mobility control scheme for a radio terminal apparatus that moves between eNode Bs, which is the technique the above-described next-generation 3GPP system is based upon, will be explained. FIG. 2 schematically shows the mobility control for when a radio terminal apparatus moves between eNode Bs. For ease of explanation, a case will be explained here using two eNode Bs.
When UE 40 accommodated in eNode B 30-1 moves to the area covered by eNode B 30-2, UE 40 transmits a transfer request to ACGW 20 via eNode B 30-2. To be more specific, UE 40 transmits a transfer request for switching the path to ACGW 20 via eNode B 30-2, in order to establish a radio link and carry out radio communication with eNode B 30-2 having stronger radio intensity than eNode B 30-1, based on the radio intensity received from eNode B 30. ACGW 20 receives the transfer request from eNode B 30-2 and switches the path, so that data directed to UE 40, which has been transmitted using path 1 by then, will be transmitted using path 2. ACGW 20 then transmits a transfer reply to UE 40. In this way, the system performs such transfer control on a UE that moves between eNode Bs.
Next, the mobility control technique shown in FIG. 2 will be explained in detail using FIG. 3. FIG. 3 illustrates the mobility control scheme in detail.
This next-generation 3GPP system 10 provides eNode B 30 with a proxy mobile agent (“proxy MA”) and ACGW 20 with a local home agent (“local MA”), using a proxy MIP, and carries out various mobile IP (mobile Internet protocol or hereinafter “MIP”)-related processings. Here, the mobile IP refers to a protocol for automatically detecting a transfer of a radio terminal apparatus between networks and for enabling the radio terminal apparatus to carry out communication in the network after the transfer in the same way as in the network before the transfer.
As shown in FIG. 3, since UE 40 is accommodated in eNode B 30-1, first, IP tunnel 1 is constructed between eNode B 30-1 and ACGW 20, and ACGW 20 and eNode B 30-1 transmit/receive data directed to UE 40 using this IP tunnel 1.
Here, when UE 40 attempts to move to eNode B 30-2, UE 40 transmits radio intensity information (i.e. measurement report) to eNode B 30-1 and reports a transfer request (step S1). This radio intensity information includes radio intensity information of UE 40 and eNode B 30-1 and radio intensity information of UE 40 and eNode B 30-2. Upon receiving radio intensity information from UE 40, eNode B 30-1 exchanges information such as resource reservation with destination eNode B 30-2, and checks whether or not eNode B 30-2 can accept UE 40 (step S2). Although this information exchange is normally carried out via ACGW 20, when, for example, eNode Bs are connected via a physical channel, direct exchange of information may be possible. When eNode B 30-2 can accept UE 40, eNode B 30-1 transmits a handover request message (i.e. handover request) to UE 40 (step S3). Upon receiving the handover request message, that is, upon receiving a transfer request to eNode B 30-2, UE 40 establishes a radio link with destination eNode B 30-2 (i.e. radio bearer setup) (step S4), and transmits a transfer completion message (i.e. HO complete) to eNode B 30-2 after having established a radio link (step S5).
eNode B 30-2 then transmits a position registration request message (i.e. MIP registration request) to ACGW 20 (step S6), and, ACGW 20 having received this position registration request message makes changes to a routing table that ACGW 20 holds inside. That is, when the destination IP address of an IP packet matches the IP address of UE 40 in the routing table, ACGW 20 changes the care of address (“CoA”) from eNode B 30-1 to eNode B 30-2, carries out IP encapsulation of the data packet, and transmits the data packet to UE 40.
ACGW 20 then transmits a position registration revocation message (i.e. MIP registration revocation) to eNode B 30-1 (step S7), and releases the resources of source eNode B 30-1. eNode B 30-1 then transmits a position registration revocation reply message (i.e. MIP registration revocation acknowledgement) to ACGW 20 (step S8). Furthermore, ACGW 20 transmits a position registration reply message (i.e. MIP registration reply) to eNode B 30-2 (step S9). Through the above-described processing, the packet directed to UE 40 after the transfer transmitted from another ACGW is transferred to eNode B 30-2 by ACGW 20.
Next, FIG. 4 shows a scheme adopting the control premised upon the above-described mobility technique disclosed in IETF RFC 3154, as a conventional paging control technique (Non-Patent Document 2).
First, UE 40 is in an idle state, and the network side knows the tracking area of UE 40. Here, a tracking area refers to the area where an ACGW accommodates an eNode B. ACGW 20 holds information about radio terminal apparatuses accommodated in the eNode B in this tracking area. Here, for example, as shown in FIG. 4, ACGW 20 knows that UE 40 is somewhere among eNode B 30-1, eNode B 30-2, . . . eNode B 30-n. 
An entity (not shown) such as an ACGW having received an IP packet of data directed to UE 40, transmits a paging request message (i.e. paging request) to ACGW 20 that accommodates the tracking area of UE 40 of the destination of the packet (step S11). Here, the entity where the IP packet is terminated once may be another apparatus connected to ACGW 20 over the Internet and so on. That is, ACGW 20 having received the data packet looks up the database of the core network (e.g., network constructed between communication systems), finds out the apparatus (here, ACGW 20) that accommodates the eNode B which accommodates destination UE 40 from the IP address of the received data packet, and transmits a paging request message reporting that the data directed to UE 40 has been received, to the apparatus.
ACGW 20 having received the paging request message performs its own paging processing, and transmits paging request messages to all eNode Bs 30 in the tracking area of UE 40 (step S12). The eNode B that actually accommodates UE 40 (here, eNode B 30-2) establishes a radio link with UE 40 (step S13), and then transmits a paging reply message (i.e. paging reply) to ACGW 20 (step S14). ACGW 20 receives the paging reply message and transmits the paging reply message to the terminating entity of the IP packet, that is, to the apparatus of the sender of the IP packet (step S15).
eNode B 30-2 performs its own position registration processing, that is, registers the IP address set in ACGW 20 of the source of the paging request, and transmits a position registration request message (i.e. MIP registration request) to ACGW 20, to establish an IP tunnel with ACGW 20 (step S16). ACGW 20 having received the position registration request message, makes changes to the routing table. Here, the CoA of the IP packet, in which the destination IP address is the IP address of UE 40, is changed such that the IP packet is transmitted to the IP tunnel of the IP address of eNode B 302. ACGW 20 then transmits a position registration reply message (i.e. MIP registration reply) to eNode B 30-2 (step S17).
Paging processing and position registration processing are completed through the above-described processing, and an incoming IP packet directed to UE 40 is delivered to UE 40.
FIG. 5 shows a functional configuration of ACGW 20 and eNode B 30 that perform the above-described paging control. First, the functional configuration of ACGW 20 will be explained. ACGW 20 is comprised of IP layer processing section 21, paging processing section 22 and proxy MIP home agent (HIP HA) processing section 23.
IP layer processing section 21 of ACGW 20 decapsulates the packet using the IP address set in ACGW 20, and receives the packet. Particularly, IP layer processing section 21 receives a paging request message from another ACGW to a radio terminal apparatus in eNode B 30 accommodated in ACGW 20, and a paging reply message from eNode B 30, and outputs these messages to paging processing section 22. Furthermore, IP layer processing section 21 receives a position registration request message from eNode B 30, and outputs the message to MIP HA processing section 23.
Furthermore, IP layer processing section 21 encapsulates the packet using the IP address set in ACGW 20, and transmits the packet. Particularly, IP layer processing section 21 transmits a paging request message (i.e. PR) inputted from paging processing section 22 and a position registration reply message (i.e. MRRly) inputted from MIP HA processing section 23, to eNode B 30.
Based on the paging request message from another ACGW inputted from IP layer processing section 21, paging processing section 22 performs paging processing, that is, paging processing section 22 tentatively stores, in page units, information whereby the paging of the destination radio terminal apparatus can be checked, from inside the paging request message. Paging processing section 22 then outputs this paging request message to IP layer processing section 21 to transfer to the eNode B that accommodates the destination radio terminal apparatus of the paging request.
MIP HA processing section 23 receives a position registration request message inputted from IP layer processing section 21, and performs position registration processing of ACGW 20. That is, in order to establish a path with the position registration request source, when the IP address of the radio terminal apparatus included in the position registration request message matches the IP address of the destination radio terminal apparatus of the paging request, MIP HA processing section 23 makes the IP address of the destination radio terminal apparatus the home address and the IP address set in eNode B 30 of the position registration request source the CoA, generates a position registration reply message to transmit to eNode B 30 and outputs these addresses to IP layer processing section 21.
Next, the functional configuration of eNode B 30 will be explained. eNode B 30 is comprised of IP layer processing section 31, paging processing section 32 and proxy MIP mobile agent (“MIP MA”) processing section 33.
IP layer processing section 31 of eNode B 30 decapsulates a packet using the IP address set in eNode B 30, and receives the packet. Particularly, IP layer processing section 31 receives a paging request message from paging processing section 22 of ACGW 20, and outputs the paging request message to paging processing section 32.
Furthermore, IP layer processing section 31 encapsulates a packet using the IP address set in eNode B 30, and transmits the packet. Particularly, IP layer processing section 31 receives a paging reply message (i.e. PRly) inputted from paging processing section 32 and a position registration request message (i.e. MRReq) inputted from MIP HA processing section 33, and transmits these messages to ACGW 20.
Paging processing section 32 receives a paging request message inputted from IP layer processing section 31 and performs paging processing, that is, paging processing section 32 tentatively stores, in page units, information whereby the paging of the destination radio terminal apparatus can be checked, from inside the paging request message. Paging processing section 32 then generates a paging reply message in response to this paging request, outputs the paging reply message to IP layer processing section 31 and triggers MIP MA processing section 33.
In order to perform the position registration processing of eNode B 30 according to the trigger from paging processing section 32, that is, in order to establish a path with the position registration request destination, MIP MA processing section 33 registers the IP address of the destination radio terminal apparatus included in the paging request message and the IP address set in ACGW 20 as the CoA for paging request source ACGW 20, and outputs the position registration request message (i.e. MIP registration request) for requesting the registration of the IP address set in eNode B 30 to IP layer processing section 31.    Non-Patent Document 1: 3GPP RAN #49 Contribution R2-052900    Non-Patent Document 2: IETF RFC 3154 “Requirements and Functional Architecture for an IP Host Alerting Protocol”    Non-Patent Document 3: IETF RFC 3344 “IP mobility Support for IPv4”    Non-Patent Document 4: IETF REFC 3775 “Mobility Support in IPv6”